1. Field of the Invention
Curable compositions, such as benzoxazine-based ones, are useful in applications within the aerospace industry, such as for example as a heat curable composition for use as a matrix resin or an adhesive, and form the basis of the present invention.
2. Brief Description of Related Technology
Epoxy resins with various hardeners have been used extensively in the aerospace and electronics industries both as adhesives and as matrix resins for use in prepreg assembly with a variety of substrates.
Benzoxazines themselves have been reported in the literature as generally having a high glass transition temperature, good electrical properties (e.g., dielectric constant), and low flammability.
Blends of epoxy resins and benzoxazines are known. See e.g. U.S. Pat. No. 4,607,091 (Schreiber), U.S. Pat. No. 5,021,484 (Schreiber), U.S. Pat. No. 5,200,452 (Schreiber), and U.S. Pat. No. 5,445,911 (Schreiber). These blends appear to be potentially useful in the electronics industry, as the epoxy resins can reduce the melt viscosity of benzoxazines allowing for the use of higher filler loading while maintaining a processable viscosity. However, epoxy resins oftentimes undesirably increase the temperature at which benzoxazines polymerize.
Ternary blends of epoxy resins, benzoxazine and phenolic resins are also known. See U.S. Pat. No. 6,207,786 (Ishida), and S. Rimdusit and H. Ishida, “Development of new class of electronic packaging materials based on ternary system of benzoxazine, epoxy, and phenolic resin,” Polymer, 41, 7941-49 (2000).
Other resins, such as reactive monomers, polymers and oxazolines, polyimide/siloxane co-polymers and cyanate esters, are too known. See e.g. U.S. Pat. No. 4,806,267 (Culbertson), in connection with oxazolines and J. McGrath et al., “Synthesis and Characterization of Segmented Polyimide-Polyorganosiloxane Copolymers”, Advances in Polym. Sci., Vol. 140, Springer-Verlag, Berlin 61-105 (1999) in connection with polybenzoxazine polyimide-polyorganosiloxane co-polymers.
Moreover, in J. Jang et al., “Performance Improvement of Rubber Modified Polybenzoxazine”, J. Appl. Polym. Sci., 67, 1-10 (1998), the authors report the use of polybenzoxazine modified with amine-terminated, butadiene acrylonitrile rubber and with carboxyl-terminated, butadiene acrylonitrile rubber to improve mechanical properties. The polybenzoxazine chosen was synthesized from bisphenol A, formaldehyde and the aromatic amine, aniline.
Notwithstanding the state of the technology, there has been no disclosure, teaching or suggestion to prepare a heat curable composition based on the combination of a benzoxazine prepared from bisphenol A, formaldehyde and alkyl amines, and amine-terminated, butadiene acrylonitrile rubber, let alone one with improved performance properties.